Our analysis of the mechanisms by which the cyclic AMP content of brain cells is regulated will be continued along three lines: 1. Agonist-induced desensitization will be studied further in an attempt to elucidate the molecular basi of the phenomenon. Attempts will be made to isolate and characterize a putative intracellular intermediate that promotes desensitization. Attempts also will be made to detect agonist-specific induction of the phosphorylation of unique membrane components that occurs concomitant with desensitization and that is lost concomitant with return of responsiveness. 2. We have established a number of experimental situations in which chronic increases or decreases in responsiveness of catecholamine-sensitive adenylate cyclase occur. We now plan to determine if changes occur in the binding capacity of such preparations for labeled Beta-receptors ligands such as I-125-hydroxybenzylpindolol and H-3-alprenolol. These studies may pinpoint or eliminate the drug-receptor interaction as the basis for changes in responsiveness to agonists. 3. We feel the chronic effects of morphine on adenylate cyclase can be explained in terms of agonist-induced changes in adenylate cyclase activity. Thus, we plan to conduct studies of the effects of morphine on agonist-induced desensitization in human astrocytoma cells, glialneuroblastoma hybrids and drug-treated intact rats. We have previously established experimental paradigms for induction of super-responsive states (to catecholamines) in intact rats. The effects of morphine on the induction of super-responsiveness in 6-hydroxydopamine-treated rats will be examined. BIBLIOGRAPHIC REFERENCES: Perkins, J.P.: "Regulation of the Responsiveness of Cells to Catecholamines: Variable Expression of the Components of the 2nd Messenger System" In: "Cyclic Nucleotides in Disease," ed. B. Weiss. University Park Press, 1975. Perkins, J.P., Moore, M.M., Kalisker, A. and Su, Y-F: "Regulation of cyclic AMP content in normal and malignant brain cells" In: Advances in Cyclic Nucleotide Research, Vol. 5, Eds. P. Greengard and A. Robinson. Raven Press, 1975.